Throughout this application various publications are referred to in parenthesis. Full citations for these references may be found at the end of the specification immediately preceding the claims. The disclosures of these publications are hereby incorporated by reference in their entireties into the subject application to more fully describe the art to which the subject application pertains.
Subjects with poorly functioning hearts can have compromised blood supply to vital organs. The pumping action of the heart and the systemic blood supply can be improved by the use of an intra-aortic balloon pump (IABP) to control an intra-aortic balloon (IAB). IABPs are used in cardiology patients and cardiac surgery patients (Baskett et al., 2002; Mehlhorn et al., 1999).
In each cardiac cycle, the IAB is inflated by means of the pumping device at the end of the ejection phase of the left ventricle of the heart, and is deflated again before the commencement of the following ejection phase. It has been suggested that systemic hemodynamics and myocardial efficiency can be improved by balloon deflation approaching or simultaneous with left ventricular ejection (Kern et al., 1999). For optimal functioning of the IABP, it is important that the IAB be inflated and deflated at the correct times in the cardiac cycle.
Methods and apparatus for controlling the inflation of an IAB have been described, for example, in Sakamoto et al., 1995; U.S. Pat. Nos. 4,692,148, 6,258,035, 6,569,103 and 6,887,206; and U.S. Patent Application Publication Nos. 20040059183 and 20050148812.
Deflation of the IAB can be triggered using the electrocardiogram (ECG) of the subject's heart (e.g., Ohley et al., 2002; U.S. Pat. Nos. 4,692,148, 4,809,681, 6,290,641 and 6,679,829). Typically, the timing of deflation of the IAB is based on the ECG trigger and generally occurs prior to the R Wave. The time for deflating the IAB can be set manually by an experienced person at a fixed time in the cardiac cycle. This manual method is predictive or historical relative to the previous ECG trigger. A disadvantage of this system is that the set deflation time will deviate from the desired deflation time with every acceleration or deceleration of the cardiac cycle, so that the deflation time constantly needs to be adjusted. Furthermore, manually setting the deflation time at a fixed point makes it difficult to properly adjust the deflation time during cardiac arrhythmia, which has unpredictable accelerations or decelerations of the cardiac cycle. Arrhythmia often occurs in subjects who require an IABP. Due to these unpredictable accelerations and decelerations of the cardiac cycle, R wave deflation of the IAB is often used during cardiac arrhythmia.
There is a need for an IABP that evaluates the likely hemodynamic results of different modes of IAB deflation and selects a deflation mode based on that evaluation to improve the efficacy of IABP therapy without the need for manual intervention by a clinician.